Inter prediction method and apparatus therefor

An image encoding method performed by an encoding apparatus, the method comprising:

• deriving spatial merging candidates for a current block when a merge mode is applied to the current block;
• constructing a merging candidate list including the spatial merging candidates for the current block;
• selecting a merging candidate from the merging candidate list;
• generating merge index information for indicating the selected merging candidate from the merging candidate list;
• generating information on a parallel merge level which represents a size of a parallel merging unit region;
• and
• encoding image information including the merge index information and the information on the parallel merge level,
• wherein the current block belongs to the parallel merging unit region,
• wherein the current block is related to a prediction unit(PU), and the PU is one of PUs partitioned from a coding unit (CU),
• wherein for the PU, within the parallel merging unit region, the spatial merging candidates are identical to spatial merging candidates of a 2N×2N PU which has a same size as the parallel merging unit region, and
• wherein the spatial merging candidates of the 2N×2N PU which has the same size as the parallel merging unit region, are derived from a lower left corner neighboring block, a left neighboring block, an upper right corner neighboring block, an upper neighboring block and an upper left corner neighboring block of the parallel merging unit region.

A non-transitory decoder-readable storage medium for storing encoded image information causing a decoding apparatus to perform an image decoding method, the method comprising:

• receiving information on a parallel merge level which represents a size of a parallel merging unit region;
• receiving merge index information;
• constructing a merging candidate list including spatial merging candidates for a current block;
• deriving motion information of the current block, based on one of the spatial merging candidates indicated by the merge index information in the merging candidate list;
• deriving prediction samples of the current block based on the derived motion information;
• and
• generating a reconstructed picture based on the prediction samples,
• wherein the current block belongs to the parallel merging unit region,
• wherein the current block is related to a prediction unit(PU), and the PU is one of PUs partitioned from a coding unit (CU),
• wherein for the PU, within the parallel merging unit region, the spatial merging candidates are identical to spatial merging candidates of a 2N×2N PU which has a same size as the parallel merging unit region, and
• wherein the spatial merging candidates of the 2N×2N PU which has the same size as the parallel merging unit region, are derived from a lower left corner neighboring block, a left neighboring block, an upper right corner neighboring block, an upper neighboring block and an upper left corner neighboring block of the parallel merging unit region.